1. Field of the Invention
This invention in general relates to photography and in particular to photographic apparatus for facilitating the coupling of a self-contained automatic camera with an optical viewing device such as an endoscope to photograph an image formed by the eyepiece of the viewing device in a manner whereby an automatic exposure control feature of the camera is advantageously preserved.
2. Description of the Prior Art
Photographic cameras of the type which include systems by which exposure of a film is automatically controlled in a predetermined manner are well-known in the prior art. In general, such exposure control systems usually comprise an electromechanical shutter arrangement that is controlled by the output of a scene brightness measuring system in such a way that aperture and/or shutter speed are set in accordance with a film's given speed rating and what the scene brightness measuring system judges the "average" scene brightness to be.
Also well-known to the prior art are optical viewing devices such as microscopes, telescopes, binoculars, and endoscopes--all instruments useful for their ability to permit visualization of details in objects which would otherwise be too distant, small, dim, or inaccessible for the unaided eye to see.
Obtaining permanent photographic records of what the eye sees through such optical viewing devices is an established practice having obvious scientific and artistic benefits. Like others, however, this photographic practice requires, among other things, that the image of the object to be photographed be available for observation immediately prior to and preferably during exposure and also must be properly exposed to record important details in the object--particularly in medical applications like endoscopic photography. These requirements are generally difficult to satisfy especially where the camera includes an automatic exposure control system as described above and does not have a reflex viewing arrangement where the image can be observed directly through the camera objective lens.
To use a camera with automatic exposure control to photograph images formed by such optical viewing devices requires that the automatic exposure control be bypassed or overridden in some way or, alternatively, coupled with the viewing device in such a way that the brightness of the image formed by the viewing device can be measured by the brightness measuring system of the camera. The alternative above, while advantageous because it preserves the camera automatic exposure control feature, presents a major problem since the viewing device image is generally hidden from the view of the camera brightness measuring system. This usually comes about because of an offset between the camera objective lens, which is generally optically aligned with the viewing device image, and the optical axis of the camera brightness measuring system. Moreover, unless the camera includes a reflex viewing device, such as those of the single lens reflex or twin reflex lens type camera, this problem becomes aggravated.
Some prior art arrangements for coupling automatic exposure control sytems of self-contained cameras with optical viewing devices show arrangements by which some part of the useful light intended for the photographic image is diverted to the photodetector of the camera automatic exposure control system through the use of branched light paths which typically utilize beamsplitters, fiber optic bundles or similar optical elements. Typical of such arrangements are those shown, for example, in U.S. Pat. No. 3,641,898 issued to Ichizo Kawakara on Feb. 15, 1972 and entitled "Electrically Driven Camera for An Endoscope"; U.S. Pat. No. 3,721,170 issued to Bruce K. Johnson on Mar. 20, 1973 and entitled "Apparatus for Adapting A Reflex Camera For Use With A Monocular Microscope"; U.S. Pat. No. 3,292,490 issued to Kenneth M. Moore on Dec. 20, 1966 and entitled "Photographic Equipment"; and U.S. Pat. No. 3,798,665 issued to Vaito K. Eloranta et al. on Mar. 19, 1974 and entitled "Apparatus For Adapting A Reflex Camera To Use With A Binocular Microscope".
Other prior art arrangements show apparatus by which a part of the image light not intended for the photographic image, but representative of the brightness of the viewing device image, is diverted to the camera automatic exposure control system photodetector or light sensing element. Such arrangements are similar to those shown, for example, in U.S. Pat. No. 3,898,678 issued to Vivian K. Walworth on Aug. 5, 1975 and entitled "Camera To Microscope Adapter With Means For Operating An Exposure Control" and U.S. Pat. No. 3,900,858 issued to Mary Conlin McCann et al. on Aug. 19, 1975 and entitled "Camera To Microscope Adapter With Special Optical Element".
Other prior art arrangements operate on the assumption that the brightness of the viewing device image is either known or can be determined independently of the camera scene brightness measuring system and that the camera exposure control system can be regulated by an auxiliary device which couples with the scene brightness measuring means of the camera in such a way that the camera shutter time and/or aperture can be regulated by a manual setting of the intensity of a surrogate scene light source. Typical of these arrangements are those shown, for example, in U.S. Pat. No. 3,696,720 issued to Billy V. Vinson on Oct. 10, 1972 and entitled "Method and Apparatus For Photographing Oscilloscope Traces With Conventional Camera"; U.S. Pat. No. 3,999,195 issued to Robert T. Little on Dec. 21, 1976 and entitled "Camera Adjustable Exposure Control Adapter"; and U.S. Pat. No. 4,021,825 issued to John J. McCann et al. on May 3, 1977 and entitled "Adapter For Operatively Coupling An Automatic Camera To An Optical Instrument". The primary objection to these latter arrangements is that they sometimes require trial and error attempts at determining the correct exposure.
Another prior art arrangement of interest is that shown and described in U.S. Pat. Application Ser. No. 955,378 filed on Oct. 27, 1978, now U.S. Pat. No. 4,192,597 in the name of Lawrence K. M. Ting for "Photographic Apparatus For Selectively Actuating A Pulsable Electronic Strobe". Here the camera shutter is controllably retained open by providing its scene brightness measuring system with a surrogate scene light while a pulsable strobe of known intensity is repetitiously fired in a known manner to illuminate the object with a predetermined level of illumination. The assumption here is that the scene will more or less always have a known brightness by virtue of always being illuminated by a known source and therefore proper exposure can be obtained by selectively varying the length of the exposure with the surrogate scene light whose intensity can be varied for this purpose. This scheme, however, can also result in trial and error attempts at obtaining proper exposure.
It is a primary object of the present invention to provide photographic apparatus by which a camera having a light sensing system which measures scene brightness to facilitate automatic exposure control can be utilized to photograph an image of an object under circumstances where the image can be presented to the camera objective lens but is otherwise hidden from the view of the camera light sensing system in a manner whereby the camera automatic exposure control feature of the camera is advantageously preserved.
It is another object of the present invention to provide apparatus of the foregoing type by which films of different speed can be used with the automatic camera.
Other objects of the invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the apparatus possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosures.